I can't disable tab completion. I absolutely hate tab completion and am desperate to get rid of it. I'm currently using a trial version of sublime text 2.

I added this to Preferences > File Settings, User:

{
'tab_completion' : false
}

And then in my CSS, I typed: color, and pressed tab. A dialog pops out giving me a list to choose from, but I don't want any. I just want to tab, not autocomplete! How do I disable it for good, or is this a bug?

What you're seeing here are snippets, which are different from tab-completion—tab-completion completes tokens by looking at other tokens in the file, whereas snippets are predefined for different languages and add chunks of code based on the tab-trigger.Add this to your user key bindings and you should be good to go in all cases:

It occurs to me that you may still want to use the tab key to indent selected text; in such a case, you can copy the relevant bindings from the default key bindings file into your user keybindings file—just put them after the previous line I sent you. That command, which takes no context argument, will wipe out all other bindings. Further bindings with a context argument will be layered on top of the most recent context-free keybinding.